Techniques are known in which the portrait of an eyeglass consumer is captured with a digital camera, the characteristics of the facial features are analyzed using predetermined software, and the form of the eyeglasses is designed by applying predetermined design rules. The eyeglass designs are determined without consideration of the differences in the eyeglass wearers' facial features or personal preferences. U.S. Pat. No. 6,533,418 B1 (Izumitani et al.) describes a system which enables a consumer to able to select many more parameters, resulting in an eyeglass design that better suits the facial features of the eyeglass wearer but with a single color or shade.
For eyewear users, particularly sunglasses but also goggles, visors and helmets, the facial features as well as color of the iris, skin and hair call for a color or shade selection that fits the iris, skin and hair color. This selection is highly dependent on the average ambient lighting level, e.g., one color fits nicely in partial darkness and a second color fits nicely in full sun. This calls for color-changing eyewear lenses made-to-order, to fit both conditions.
For aesthetic and utility reasons, some people would like their glasses to have a preferable color or shade when used indoor or in low sun light flux and have a different color or shade when used outdoors or in high sun light flux.
Most common eyewear have usually a certain permanent color or shade having a predetermined optical density that is constant during the eyewear lifetime.
Some of the eyewear have a permanent color or shade, but also have a variable optical density that changes when exposed to, e.g., ultra-violet (UV) light. These are called photochromic glasses, that become less transmissive when exposed to the activating light.
Transparent materials that change their color or shade when exposed to light are known as photochromic materials. Some plastic ophthalmic lenses involve embedding a solid layer of photochromic mineral glass within the bulk of an organic lens material. Examples include U.S. Pat. No. 5,232,637 (Dasher et al.) that teaches a method of producing a glass-plastic laminated ophthalmic lens structure, and U.S. Pat. No. 4,300,821 (Mignen et al.) that teaches an ophthalmic lens made of organic material having at least one layer of photochromic mineral glass within its mass to impart photochromic properties to the lens.
Transparent materials that change their color or shade when exposed to temperature changes are known as thermochromic materials. The thermochromic dyes commonly used are spirolactones, fluorans, spiropyrans and others.
The present invention relates to the colors of eyewear lenses, and more particularly, to eyewear lenses having a change in their transmitted and reflected color or shade, where the change is due to changes in the flux of the solar impinging light and/or the environmental temperature of the glasses. The invention is also applicable to color-changing windows, including car windows.